Cuticular hydrocarbons, isoenzymes and behavior of three populations of Anopheles darlingi from Brazil.

Three populations of Anopheles darlingi were studied for cuticular hydrocarbons, isoenzymes and patterns of peak biting activity. Differences were found in specimens from Costa Marques, a malaria endemic area; Dourado, a site with a very exophilic population and Juturnaíba, located near the type locality. Twelve hour collections from sunset to sunrise showed that An. darlingi from Costa Marques had a bimodal biting activity profile with a major peak at sunset and a minor peak at sunrise. At Dourado, the pattern was trimodal, with peaks at both morning and evening periods of twilight and near midnight. The Juturnaíba population showed a slight increase in activity near 2000 and 0100 h. Nei's genetic distances, determined by isoenzyme electrophoresis between pairs of populations, were low (D < or = 0.049). Using discriminant analysis for the cuticular hydrocarbons, 92.4% of the specimens from Costa Marques, 91.2% of the specimens from Dourado and 61.3% from Juturnaíba were correctly identified. Cuticular hydrocarbon and isoenzyme results matched very well: the smaller the Nei's distance, the more misidentifications occurred in the jackknife estimator used in the cuticular hydrocarbon analysis. This is the first report of cuticular hydrocarbon analysis in combination with isoenzymes to investigate neotropical anopheline species.

Intraspecific variation in the cuticular hydrocarbons of the sandfly Phlebotomus perfiliewi from Italy.

The cuticular hydrocarbons of Phlebotomus perfiliewi Parrot from representative localities on both sides of Italy show contrasts which support the view of Ward et al., (1981) that there are distinguishable populations of this sandfly on the Adriatic and Tyrrhenian coasts. It is suggested that the Appennine mountains form a barrier between the Adriatic and Tyrrhenian populations. A third distinct hydrocarbon type of P. perfiliewi was detected in Calabria, southern Italy, where contact between the Adriatic and Tyrrhenian types of flies is most likely to occur. P. perfiliewi from a trans-Appennine pass were also of the Calabrian hydrocarbon type. These hydrocarbon contrasts between allopatric populations of P. perfiliewi may result from clinical variation across the Appennines, associated with different host preferences, or they may represent apomictic populations with differential mate recognition systems.

Separation of Psychodopygus carrerai carrerai and P. yucumensis (Diptera: Psychodidae) by gas chromatography of cuticular hydrocarbons.

Specimens of two species of sandfly, Psychodopygus carrerai carrerai and P. yucumensis, vectors of Leishmania braziliensis braziliensis in the subandean lowlands of Bolivia, were subjected to cuticular hydrocarbon analysis to ascertain if the technique could separate the females. A high degree of separation (87%) was obtained based on significant differences in the cuticular hydrocarbon composition of these two species. Statistical treatment of the data shows that these species, initially identified by the colour of the mesonotum, can also be distinguished by their hydrocarbons.

Impact of permethrin-treated bednets on malaria transmission by the Anopheles gambiae complex in The Gambia.

Malaria vector mosquitoes belonging to the Anopheles gambiae complex were studied in four hamlets in The Gambia. All inhabitants were given bednets treated either with a placebo (milk) in two hamlets or with the pyrethroid insecticide permethrin (500 mg/m2) in two other hamlets. Malaria transmission occurred mainly during a few weeks of the rainy season, in September and October 1987. The indoor resting densities of mosquitoes in permethrin-treated hamlets were reduced, and we estimated over 90% reduction in biting on man by An. gambiae Giles sensu stricto in these hamlets. No mosquitoes were found under permethrin-treated bednets compared with eighty-one recovered from placebo-treated bednets. Mosquitoes exited more readily from rooms where permethrin-treated bednets were used than from rooms with placebo-treated nets. The annual mean probability that a child would receive an infective bite was estimated to be 0.09 in hamlets with insecticide-treated bednets, compared with 1.9 where placebo-treated bednets were used. Permethrin-treated bednets are therefore recommended as a means of effectively reducing the risk of exposure to malaria transmission, particularly in areas of low seasonal transmission.